在幻灯片http://www.slideshare.net/billkarwin/models-for-hierarchical-data,我看到了一个SQL代码(第22页):SQL查询优化
INSERT INTO Comments (author, comment)
VALUES (‘Ollie’, ‘Good job!’);
SELECT path FROM Comments
WHERE comment_id = 7;
UPDATE Comments
SET path = $parent_path || LAST_INSERT_ID() || ‘/’
WHERE comment_id = LAST_INSERT_ID();
我认为我们可以优化它:
SELECT path FROM Comments
WHERE comment_id = 7;
INSERT INTO Comments (author, comment, path)
VALUES (‘Ollie’, ‘Good job!’, $parent_path || LAST_INSERT_ID() || ‘/’);
我说得对不对?
插入中LAST_INSERT_ID()的值是多少? – Glenn
我认为插入语句的ID。看看幻灯片。 –
但是在优化语句中没有以前的插入语句,只有一个select语句。 – Glenn